low voltage ac-dc step up help

[kiprak]

i'd like to start by introducing myself,
my names nick and i like to tinker.

to the point, I'm looking to build a circuit that can capture low ac voltage (.1v-5v ac) from an induction generator and turn it into dc volatage (10v dc).
efficiency is veryyyyyy important.

I have very little electronics experience, although more than the average but I think something using mosfets would work or maybe a full wave rectifier diode...
any help is greatly appreciated.
-Nick

 

[chemelec]

Not very Practical or even Possible, unless your AC Voltage has Lots of Current.

 

[ronsimpson]

https://www.linear.com/product/LTC3105 This looks good.
https://www.linear.com/product/LTC3109
https://www.linear.com/product/LTC3108
https://www.linear.com/product/LTC3107

 

[kiprak]

Ya, my idea is to trickle charge a capacitor or something until the voltage gets high enough to power the device for a minute or so.
this sound right?

 

[kiprak]

what i'm trying to do in short is harvest small amounts of energy until the stored capacity grows to a point that is useable for powering a device for a short amount of time.

 

[crutschow]

Ronsimpson's references are good for turning low voltage DC into higher voltage DC. But before that there is the problem of efficiently converting the AC to DC. The obvious solution for that is to use an efficient transformer to raise the voltage to the point where Schottky diodes or MOSFETs used as rectifiers can be efficiently used.

What is the lowest frequency of the AC from the generator and what is its current?

 

[kiprak]

.1 amps and 20mv

 

[kiprak]

.01 amps at 20mv

 

[crutschow]

You do realize that converting .01A @ 20mV to 10V means the current is reduced to 20 microamp even with 100% efficiency.

 

[kiprak]

I understand. at its lowest the voltage will be 20mv at its highest it will be 4 volts. when the generator is operating normally around 2-3 volts at .01 amps.
the idea I have is to capture the energy like coins in a coinbank. over time the charge will build to a point it is useable.

 

[dr pepper]

A joule thief circuit will convert 0.6v or so to a higher volatge, usually only 70% efficient, do a google for joule thief, if you want nore efficiency than this then you'll need some in depth electronics knowledge.

 

[alec_t]

A joule thief circuit will convert 0.6v or so to a higher volatge

Alas, only if the input is DC; not 20mV AC as the OP requires.

 

[dr pepper]

Oops yes missed that.
Maybe a fet bridge rectifrier with very low vdrop would be the ticket, then again nope threshold voltage messes that up.

 

[kiprak]

the threshold voltage is not super important. 200mv would be fine as well if that helps. even a half volt threshol would work for my application.

 

[dr pepper]

DC to Dc upconconverters I've seen in ic form start working at 1v, a blocking oscillator joule thief type circuit with a singlee transistor assuming silicon is used will start working around 0.6v, maybe a little less, germanium transistors (only good for low power) will start to work around 0.3v, maybe a little less.

 

[ronv]

Did I miss it? What is the frequency of your generator?

 

[kiprak]

Not sure what you mean by frequency. can you clarify? are you asking the hz? that is variable as its a bouncing magnet moving through insulated copper wire.

would it be easier to first up convert the ac to higher voltage ac before converting it to dc?

 

[ronsimpson]

So it is like a "shake flashlight".
The LTC3109 in post #3 clams it will work to 30mV and auto sense polarity which might be like "AC". I have seen it work at 50mV.
If you could run form 0.5 to 5 volts then I know another way to do that.

 

[kiprak]

exactly the same generator in a shake flashlight.
am I mistaken to think this is ac?
.5v to 5v would work as well.

 

[ronsimpson]

This will probably not work for you but there might be an good idea in it.

I have a high voltage low current source. This does work. The diodes loose 0.4 volts.
In your case it will convert the AC to DC. Then store anything above 0.4 volts on a capacitor.
The DC to DC converter will make a regulated supply for running a micro computer or small radio.
If there is more energy than needed the power is stored for later use.